(1) Field of the Invention
The invention relates to synchronization of signals. More specifically, the invention relates to retiming of incoming video signals to match a reference video stream.
(2) Background
Video signals are composed of a number of horizontal lines which contain horizontal synchronizing information. A group of horizontal lines forms a frame or a field. The group that forms the field or frame is determined by a vertical synchronizing information (VSI). The VSI is embedded in the video stream. Interlaced video includes two fields of horizontal lines with the second field offset by a half line, such that when displayed simultaneously, greater resolution can be achieved. Typically, the first field of the interlace is received entirely before the second field of the frame begins to arrive. The two fields together form one interlaced frame. Each of the fields has its own associated VSI. Often, a digital video stream is desired to be synchronized with a reference video stream of the same clock frequency. To accomplish this, the incoming video stream needs to be delayed enough such that the frame or field boundaries (VSI) embedded in the two streams are coincident. Accomplishing this alignment in an automatic fashion without operator intervention has proven problematic.
A method and apparatus for retiming video is disclosed. Vertical synchronization information (VSI) is detected in an incoming video stream. A VSI is also detected in both as output video stream and a reference video stream. Based on the difference between the VSI of the reference and output video stream reads or writes to a FIFO are suppressed until the VSI""s are coincident.